You mean this Einstein?
Posted on 06/23/2003 9:25:12 AM PDT by RightWhale
There are four fundamental forces in nature:
Strong force
Weak force
Electromagnetism (EM) Light is an electromagnetic wave
Gravity
All of the fundamental forces are considered Exchange Forces. In other words the force involves an exchange of one or more particles.
The exchange particles are as follows:
Strong – The pion (and others)
Electromagnetic (EM) – The photon
Weak – The W and Z
Gravity – Believed to be the graviton
An addition by Physicist:
Note: The pion does mediate the inter-nucleon force. That force isn't fundamental, however. The fundamental force is the inter-quark force that binds the quarks into hadrons (such as protons, neutrons and pions), and that is what we usually mean by the strong force, nowadays. The force between hadrons is a residual color dipole interaction that is analogous to the Van der Waals force in electromagnetism.
Exactly - that's the whole basis of the miracle bra / underwire theory.
If the speed of gravity were infinite you could use gravitational effects to synchronize the clocks in two different frames. This leads to contradictions to the principle of relativity, even in special relativity.
For example, if spaceships pass each other moving in opposite directions, each appears to be contracted relative to the other.
However, by stationing observers at opposite ends of both ships with synchronized clocks, we could determine which ship was "really" contracted and which merely appeared contracted by observing the times at which observers on each ship passed their counterparties.
The argument has superficial plausibility but has been convincingly refuted by (e.g.) Prof. Carlip at UC Davis.
The basic argument relies on something like the inverse of the Poynting-Robeson (spelling?) effect. Light moving radially from the sun encounters Earth moving 'forward' and thus falls at a slight angle relative to the radius vector from Earth to Sun. The effect of this is to exert a slight retrograde pressure due to Earth's motion relative to the radial lines from the Sun.
Gravity, it is argued, would have the same vector triangle except that it would be of opposite sign (since gravity 'sucks' and light 'pushes'). This, says the argument, should cause an acceleration of Earth relative to the Sun, which in a remarkably short period of time (a few thousand years) would result in a doubling of Earth's orbital distance, and in millions of years would fling us out of the solar system entirely. Therefore gravity must propagate at infinite speed, QED.
The problem is that it can be shown that under General Relativity, gravity waves are radiated which exactly equal the increased energy due to the 'couple'. The extra momentum, in other words, is leaked away via gravity waves and the solar system remains stable.
--Boris
Glad you cleared that up.
Assuming this is going on, should we expect to be able to detect these gravity waves somehow? They would be coming from all directions and we ought to notice them if they are 'bright' enough and perhaps even form images. Or are they so weak and smooth that we can't devise instruments sensitive enough to register them?
Maybe gravity waves propagate at a finite speed. However, they are unlike light in that: light is generated by various reactions and must be generated or it goes out, ceases, whereas gravity is always just there, static, not necessarily propagating at all. Maybe gravity waves are possible, but just an ancillary phenomenon, something that gravity can do but doesn't need to do.
You'll probably be just like Einstein and give all the money to your first wife.
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